The present invention relates to the recovery of amine from amine-containing spent acid stripping liquor for obtaining an aqueous liquor effluent that meets economically today's stringent quality standards and for recovering amine therefrom for reuse in a variety of chemical processes.
Vaporous amines can be scrubbed from vaporous or gaseous streams bearing same by several techniques including, for example, adsorption by a solid adsorbent, scrubbing by an acid scrub liquor, or similar techniques. Such vaporous amine effluents can arise from a variety of commercially practiced chemical operations, such as, for example, cold-box foundry core and mold production and vapor permeation curable coatings. Cold-box foundry core and mold production involves the admixture of a binder with sand or similar foundry mold particulate aggregate which is molded into a desired shape followed by its exposure to a vaporous amine gas stream. Such foundry binder cold-box technology can be found in, for example, U.S. Pat. Nos. 3,409,579; 3,429,848; 3,485,797; 3,676,392; 3,933,727; and 4,179,427. Vapor permeation curable coatings involves the application of a coating composition comprising an aromatic-functional polymer, a polyisocyanate, optionally dispersed in a solvent therefor, which coating composition is exposed to a vaporous tertiary amine to achieve rapid, room temperature cure of such coating. Exemplary vapor permeation curable compositions and processes can be found in U.S. Pat. Nos. 3,789,044; 3,822,226; 3,836,491; and 4,331,782 and British Pat. Nos. 1,369,351 and 1,351,881.
The gaseous amine-containing stream vented from the foundry core box or from the vapor permeation cure chamber bears amine therein which poses an environmental disposal problem. Stringent quality standards require the amine to be removed from such vapor stream prior to its being vented to the atmosphere. While solid adsorbent techniques could be employed, current foundry thinking involves the use of acid scrubbing liquors through which the spent amine gas is passed or bubbled. The acid in the scrub liquor reacts with the amine to form the corresponding amine acid salt and leaves the carrier gas stream of suitable quality for its venting to the atmosphere. Such carrier streams can be air, carbon dioxide, nitrogen, or similar conventional carrier gas. The stripping liquor, however, presents its own disposal problems. Heretofore, such spent stripping liquor has been sent to environmentally-approved waste disposal sites or stored in drums or tanks at the plant site while disposition thereof is decided.
The spent stripping liquor involves not only a waste disposal problem but also represents a loss of valuable amine. The present invention is directed to a simple and economical process for recovering the amine from such spent stripping liquors in a form suitable for reuse, eg. by the foundry industry or by the vapor permeation curable coating industry.